The Proceedings of the Symposium on sports and human dynamics
Online ISSN : 2432-9509
Current issue
Displaying 1-49 of 49 articles from this issue
  • Naoto MIYAMOTO, Keizo YAMAMOTO, Satoshi MORI, Ryuji MIURA, Nozomu HATA ...
    Session ID: A-2-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
    CONFERENCE PROCEEDINGS RESTRICTED ACCESS

    In order to improve the flight distance of a ski jumping, the lift-to-drag ratio must be maximized in all phases of the flight. Recently, high-accuracy positioning using kinematic GNSS becomes common, which achieves accuracy at centimeter-level by using carrier-phase enhancement. The purpose of this study is to apply the kinematic GNSS to analyze aerodynamic characteristics in all the flight phases of ski jumping. We have developed a wearable post-processed kinematic (PPK) GNSS receiver named AT-H-02 and measured a ski jumping at the Okurayama jump stadium in Japan. In order to improve the positioning accuracy, we have developed a select method of the GNSS satellites that can eliminate signals deteriorated by jumping hill. By using this method, the fix rate during flight of a ski jumping improved more than 20% and achieved 97.7%. Based on flight trajectory of the ski jump obtained from the AT-H-02, we have successfully calculated the aerodynamic characteristics in terms of lift force, drag force and lift-to-drag ratio.

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  • Shunya UDA, Msaki TAKEDA, Naoto MIYAMOTO
    Session ID: A-2-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Cross-country skiing is broadly divided into classical and skating techniques, and skating techniques combines several types of sub-techniques such as quick skating (V1), super skating (V2), and rabbit skating (V2a). These sub-techniques require you to choose the most appropriate technique for the occasion in consideration of the inclination of the course, snow quality, speed, and your own physical strength (upper body power). Purpose: We use a high-precision kinematic GNSS to discriminate between the sub-techniques of the skating technique. Methods: One male athlete who had represented the cross-country skiing Japan the cross-country event at the Winter Olympics was analyzed during skating style 3.0 km time trial recorded with a high-precision kinematic GNSS attached to the skier’s head. A video camera was mounted on the lumbar region of the skier to detect the type and number of cycles of each technique used during the entire time trial. Based on the GNSS trajectory, distinct patterns of head displacement (up-down head motion and moving direction) for each skating technique (e.g., V1, V2 and V2a) were defined. Results: The %Match was high: 101.5 % for V1, and 94.1 % for V2, and 97.1 % for V2a, and 98.8 % in total. Conclusions: It was suggested that a high-precision kinematic GNSS can distinguish the sub-technique of the skating techniques by combining it with the trajectory analysis of the left and right movements as well as the up-and-down motion of the head.

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  • Sande GAO, Naoki UENO
    Session ID: A-3-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    In ancient times, blowgun was used as a simple ranged weapon to hunt small animals. Today it is mainly used for sport wellness in Japan and is called Fukiya. The underlying principles of blowgun, especially the dynamic behaviours of the dart and the airflow in a blowpipe have not been studied sufficiently. In order to assist the design of new sport wellness blowguns, in particular, to design a dart which can travel horizontally in the blowpipe with small air resistance and can fly along a desired direction and distance, experiment and computer simulation for sport wellness blowgun were carried out. The experimental apparatus consists of the blowing system and high-speed video camera system. The blowing system is composed of a dart, a blowpipe, a mini digital angle meter and a compressor. The high-speed video camera system is composed of a video camera, a control unit, a synchronizing unit, an analog-digital converter, and a personal computer.

    A moving particle simulation (MPS) software called Particleworks was used in the computer simulation.

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  • Kazuya SEO, Tubasa HANEISHI, Shinichiro ITO, Masaki HIRATSUKA
    Session ID: A-3-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Bayesian optimization of the flight distance for sizes of a javelin was carried out. The procedure is divided into three parts. The first step is to calculate aerodynamic forces acting on a javelin. This was carried out with the aid of CFD. The second step is optimization of the flight distance for launch conditions. The longest flight distance for optimal launch condition was obtained. This was carried out with the aid of a genetic algorithm. The third step is Bayesian optimization of the flight distance for sizes of the javelin. It was found that the optimal sizes of the javelin driven by Bayesian optimization were almost comparable with those of commercially available javelin.

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  • Hayato TATEYAMA, Daichi YAMASHITA, Satoshi Ohashi, Akira SHIONOYA
    Session ID: A-4-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Jump training plays an important role in sports training, and RSImod, the ratio of jump height to movement time, is used to evaluate the neuromuscular characteristics of athletes. In a previous study, the influence of feedback was evaluated by training with only the RSImod as feedback, but it has been suggested that this feedback has a negative effect when athleticism is emphasized. In this study, we evaluated the effects of feedback on the subjects by simultaneously providing feedback of RSImod and jump height and setting a standard for jump height. The experiment was conducted on nine subjects, three in the group without feedback and six in the group with feedback on RSImod and jump hight. In the group with no feedback, the subjects changed their posture to a one in which they sank deeper and jumped higher. However, it was difficult to extend RSImod, which is a hidden parameter, and no subject increased RSImod. On the other hand, the subjects with feedback were trained to increase RSImod. The subjects were able to confirm the change in RSImod for each trial in response to their own jumps, and all subjects were able to confirm an increase in RSImod. Previous studies have shown that, it is important to shorten the movement time to increase RSImod even if the jump height is lowered. However, in the present study, the jump height was set as a criterion, and most subjects changed to increase RSImod while also increasing the jump height. This may be due to the feedback given in this study, and it is thought that the effect of highly competitive training was obtained. In the future, we will increase the number of subjects and conduct more quantitative evaluations. In addition, the relationship between posture and jumps will be clarified based on the relationship between the posture data obtained from videos of postures during the pre-test and post-test and the measurement values obtained in this study.

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  • Zeming JIN, Takeo MARUYAMA
    Session ID: A-4-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The purpose of this study is to verify the validity of estimation of lower limb muscle activity during jumping by a musculoskeletal simulation model. The data of the measurement experiment was used as the input data of the simulation, and the lower limb muscle activity was calculated by the simulation. Three types of jumps (Squat Jump, Drop Jump and Countermovement Jump) were performed, and the EMG data of the rectus femoris, long head of biceps femoris, lateral gastrocnemius, and tibialis anterior, selected by correlation analysis, were measured, and compared with the simulation results.

    Validation results showed that the Gait2392 simulation model underestimated the muscle activity, but a similar curve to the measurement experiment. The model is considered to have sufficient validity. Therefore, the reliability of estimating muscle activity during jumping using a simulation model was confirmed. However, the first half of the landing stage of the jump has a slight difference in the simulation results, and it is thought that it is necessary to analyze the landing stage in detail.

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  • Ayane KUSAFUKA, Naoki TSUKAMOTO, Kohei MIYATA, Kazutoshi KUDO
    Session ID: A-6-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    In the motion capture systems of humans, reflective markers attached to the body have widely been used to track them by optical cameras. However, when the speed of motion increases, as the camera's angle of view and brightness are limited and the markers often fall off, especially for detailed body parts such as fingers in full-body movements, other parts of the body (palms) have been investigated instead. In this study, we attempted to acquire finger movements in high-speed throwing motion without attaching markers using automatic image recognition technology based on deep learning (DeepLabCut), and verified its accuracy comparing with conventional methods. As a result, the absolute distance between 3D coordinates obtained from the two motion capture systems was an average of 15.5 mm ~ 29.4 mm depending on tracked points and the correlation coefficients between them ranged 0.932 ~ 0.999. Therefore, the shapes of the time-series profiles of 3D coordinates obtained from the two motion capture systems were similar. These results suggest that motion measurement using markerless motion capture is possible in environments where it has been difficult to use conventional motion capture systems.

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  • Yuwei YIN, Takayuki AOKI, Seiya WATANABE, Masayoshi NIWA, Hiromichi KO ...
    Session ID: A-6-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The aerodynamics of baseballs with gyro spins and their influences on the flight trajectories are studied. We use a simulation code based on Lattice Boltzmann Method with the cumulant collision term which works for a LES model. We analyze 2- and 4-seam orientations for gyro-spin balls according to the actual MLB pitches. Both results exhibit periodicity of lift forces. We also compute 2- and 4-seam orientations for back-spin according to compare them with the gyro-spin balls. In the case of back-spin balls, both exhibit longitudinal lift forces because of the magnus effect. In the case of gyro-spin, the time-averaged lift forces are almost zero. The trajectory of above 4 kinds of rotation is studied and the longitudinal displacement of the gyro-spin ball is largest among them. It is understood that aerodynamics of back-spin and gyro-spin balls are quite different, and the seam orientations have strong effects on the aerodynamic and flight trajectories.

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  • Takuya HONDA, Takayuki KOIKE, Masaaki OKAUTI
    Session ID: A-6-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    This study aimed to investigate how the changes in trunk posture affect pitching performance in experienced baseball players. The five experienced university baseball players participated in this study. We asked subjects to perform the pitching with two conditions of trunk postures, as the throws were made as usual without any instructions (NT: normal throws) and throwing with slouched posture by relaxing trunk muscles (ST: Slouched throwing). Their pitching motion was collected in an indoor room with four high-speed cameras, located in front of the pitching direction (right and left) and reverse side of the direction (right and left), with 250 fps and a shutter speed of 1/1000 sec. We calculated angular velocities and several torque components about the pitching arm and trunk. We found that, during the ball releasing phase, significant positive correlations between the hand tip velocity and the elbow extensor velocity and between the tip velocity and elbow flexor interaction torque were obtained in the NT, while in the ST, a significant positive correlation between the hand tip velocity and palm flexor angular velocity, and between was obtained. The findings indicate that the difference in the trunk posture affected pitching movement in several joints and torque exertion in the elbow joint for increasing ball releasing velocity.

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  • Taishi OKEGAWA, Ayane KUSAFUKA, Shimpei KUBO, Takehiro FUKUDA, Kimitak ...
    Session ID: A-6-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
    CONFERENCE PROCEEDINGS RESTRICTED ACCESS

    The purpose of this study was to examine muscle activity that does not positively affect pitch velocity by comparing throwing arm muscle activity during full strength and force-regulated pitching. Subjects threw a baseball at 80% and 100% subjective intensity. Muscle activity of the biceps brachii (BB), triceps brachii (TB), flexor carpi ulnaris (FCU) and extensor carpi radialis (ECR) muscles was measured using a wireless EMG measurement system (Trigno wireless EMG system: Delsys Inc.) and compared between conditions. The co-contraction index (CCI) was also calculated during the comparison. Despite significant differences in velocity between the two conditions, there was no difference in throwing arm muscle activity or forearm co-contraction index from 190 ms before release to release. Upper arm co-contraction index was higher when throwing at full speed. Furthermore, we also analyzed whole-body muscle activity and found differences in lower extremity/trunk and nonthrowing arm muscle activity. The results of this study provide new insights into the motor control mechanisms that regulate pitch velocity in skilled pitchers.

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  • Ami KUROMARU, Takeo MARUYAMA
    Session ID: A-7-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    This research aims to construct a system that can be used for simple movement analysis and instruction in the studio and on stage to improve performance in classical ballet. For this purpose, it is necessary to verify whether it is possible to evaluate motion from 2D data of moving images. In this study, body angles of the three joints of the lower limb were calculated using Pose-cap for the ballet grand jeté movement and compared with 3D movement data. The purpose of this research was to verify the validity and accuracy of the motion evaluation method using 2D motion data. The result showed that there was no correlation between 2D and 3D motion data in the air, but there was a positive and significant correlation for body angle during landing. The speed of movement in the air is faster than when landing, and it may have been difficult for the AI to recognize the movement when the frame rate was 30Hz.

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  • Keita MINAMIZONO, Taiga YAMASAKI, Xin XIN, Shinsaku IZUMI
    Session ID: A-7-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The ‘moonwalk’ (backslide), known as a dance step or pantomime technique, is a movement in which the feet slide backward on the floor, while it gives the observer the illusion of walking. In this research, we investigate the characteristics of the moonwalk from the measurement using a motion capture system and force plates, and propose a kinematic model of the moonwalk to generate trajectories similar to the measured movement under its kinematic constraints.

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  • Ken OHTA, Takehiro FUKUDA, Toshitaka KIMURA
    Session ID: A-7-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Speed and accuracy are both critical to sports performance but remains poorly understood. In baseball pitching, both ball speed and accuracy must be constrained by human body and ball dynamics. This study examines the dynamics of pitching control ability that coordinates ball speed and control using the center of curvature of trajectories of ball and shoulder joint. Dynamics analysis based on a variable-length pendulum model with the center of curvature of the ball and shoulder joint trajectories reveals that the control of shoulder acceleration affects the coordination of ball speed and pitch control.

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  • Kodai OZAKI, Takayuki KOIKE, Masaaki OKAUCHI, Takuya HONDA
    Session ID: A-8-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    One of the representative injury mechanisms of anterior cruciate ligament (ACL) injuries and tears, which are serious sports injuries, involve knee valgus that occurs during landing from jumping and side cutting movement. This study aimed to investigate the risk factor of ACL injury or rupture by using the multi-directional landing motion, which is believed to induce the injury or rupture. We captured 3D joint displacement using four high–speed cameras and calculated joint angle in the lower extremity and torso from initial ground contact (touchdown) to the time of peak vertical ground reaction force found. While there were no differences in the knee valgus displacement after landing regardless of differences in landing direction, there was a strong positive correlation between the knee valgus and the external rotation of the knee in all landing directions, both for the dominant and non-dominant leg. This suggests that as external rotation of the knee increased, knee valgus increased. We also found that, at touchdown, a positive correlation between knee valgus and hip flexion (0° direction), and also between knee flexion (30°, 60°, 90° directions) in the dominant foot, and a positive correlation between knee valgus and hip external rotation (0°, 30°, 60°, 90° directions) in the non-dominant foot. The results suggest that increases in the knee valgus was due to the increases in the knee flexion in the dominant foot, and the increases in the hip external rotation in the non-dominant foot at touchdown.

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  • Daichi NAKAMOTO, Toshimasa YANAI
    Session ID: A-9-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The purpose of this study was to propose a method for describing the rotational motion of the entire golf swing by two lines about which the trunk and the lower limbs rotate respectively, and to visualize individual differences in the rotation axes. Three-dimensional whole-body motion data of three male golfers were collected using an IMU motion capture system and a helical axis was computed for each body segment at each interval of frames. The weighted average of the helical axes of the head, upper trunk, and lower trunk segments was computed for each interval to represent the rotation axis of the trunk. Similarly, the weighted average was calculated for femur, leg, and foot segments to represent the rotation axis of the lower limbs. The mean values and standard deviations of the position and orientation of each rotation axis were computed over each of the two swing phases (backswing phase & downswing phase) and animated as cones in computer graphics. Comparisons of the rotation axes among the three golfers revealed that the position and the direction of the axes are unique to each player.

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  • Yudai KIMURA, Ran DONG, Soichiro IKUNO
    Session ID: A-9-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Golf swing analysis is mainly performed using a high-speed camera and a device called a Trackman. Trackman can collect club data, ball data, putting data, etc., and the high-speed camera can record images at 6000 Hz. However, these devices are quite expensive and difficult to introduce to the general golfer. This research adopts an inexpensive inertial motion capture, Perception Neuron 2.0, to numerically capture motion and identify the differences between motions that result in straight and slice ballistics. In general, the left half of the body opening, and the head up are known to cause a slice ballistic of the golf ball. In this research, the analysis focuses on the front left half body and the head motion. The captured golf swing motion data is then processed by Hilbert-Huang Transform to calculate their instantaneous frequency and instantaneous amplitude. The result of the research found differences at the moment of impact of the golf swing at low frequencies. The amplitude of the straight ballistic motion of the head and the left shoulder increases at the moment of impact of the swing. On the other hand, the amplitude of the slice ballistic motion of the head and the left shoulder increases before impact. These results indicate that the slice ballistic motion is causes by an opening of the left half of the body and head-up from a biomechanical viewpoint.

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  • Harutoshi YUKAWA, Batbayar SHAGJ, Shozo KAWAMURA
    Session ID: B-1-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The purpose of this study is to consider the two-dimensional impact force applied to the artificial turf with spike studs, especially focused on the horizontal impact force. The shock attenuation properties of sports surfaces are usually evaluated by reduction of maximum input force, for example, WA (World Athletics) adopted the EN14808 as the vertical force attenuation test. Otherwise, the horizontal impact attenuation has not been treated as the regulation of impact, although the most of impact in sports activities performed with diagonal impact force, including horizontal impact forces. In previous studies, we developed the two-dimensional impact test device with parallelogram structure which divide the vertical impact force to two-dimensional impact forces simultaneously. The impact test device can be set the various impact weights to generate the impact forces resembled to the ground reaction force in human running. And proposed the method for two-dimensional impact attenuation, named DFR (dynamic force reduction) because the horizontal impact forces were very dependent to the initial impact angle. Although the proposed method could evaluate the attenuation of various impact forces, there are some inappropriate cases especially in horizontal impact force attenuation. As the results, the horizontal impact force is very dependent to the impact angle and is independent to the vertical impact attenuation properties. Additionally, rubber chip as an infill material may cause increasing of horizontal impact force because it makes larger horizontal displacement in diagonal impact.

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  • Masataka IWAI
    Session ID: B-3-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    It is known that a phenomenon in which a respiratory rhythm coupling with a locomotor rhythm (LRC: locomotor-respiratory rhythm coupling) occurs during running. At this LRC, the respiratory rhythm rate increases in proportion to the locomotor rhythm intensity, and when it approaches the limit locomotor rhythm intensity, an unstable phenomenon of the respiratory rhythm increases becomes sometimes observed. This instability of the respiratory rhythm causes lower exercise efficiency, so it is necessary to keep the stable respiratory rhythm up to the faster locomotor rhythm as far as possible. Therefore, we obtain a model with a locomotor rhythm added to the nonlinear differential equation that expresses the respiratory rhythm. We consider a method of a central command to suppress the instability of the LRC for this model. By simulation, we show LRC, the instability of the LRC, and the central command to suppress this instability.

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  • Takayuki KOIKE, Satoshi HASHIMOTO, Masaaki OKAUCHI
    Session ID: B-3-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The aim of this study was to investigate how grasping dumbbells during a countermovement jump (CMJ) affects kinematic variables like jumping height and arms swinging motion, and kinetic variables like ground reaction force and joint torque components in the lower and upper extremities. Twelve male students participated in this study and performed CMJ with and without grasping dumbbells for 0kg, 1kg, 2kg, 3kg, and 4kg. We captured their CMJ movement using a high-speed camera (300fps) and ground reaction force during CMJ using a force platform (1000Hz). Then, segment and joint angles and torque components in the lower and upper extremities. We found that while no significant changes in jumping height and joint torque in the lower extremity between each dumbbell condition were obtained, significant decreases in the angle at the toe-off, angular displacement during the arm swing phase in the shoulder joint, and some torque components as muscle and Coriolis torques in the shoulder and elbow joints as dumbbell mass increased. On the other hand, contact duration and the impulse of vertical ground reaction force during the ascent phase of jumping were increased. The findings indicate that the shoulder joint responded to the changes in the mass of the dumbbell by decreasing angular displacement and torque components such as muscular and Coriolis torques. If subjects continued CMJ with grasping dumbbells, muscle and Coriolis torques about the shoulder joint would be enhanced, and jumping height would increase.

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  • Hyougo OHSAKI, Kenji NAKASHIMA, Fuminori MATSUYAMA, Yuuki JOHNO, Takas ...
    Session ID: B-4-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    In the top league of rugby, players are worn with IMU sensors that record their kinematic characteristics, and they are searching for effective ways to utilize the data. We focus on tackling motions and aim to develop an AI that extracts and evaluates signals corresponding to tackling motions from the signals measured by inertial sensors. This study analyzed wearable IMU data and video data collected from official matches played by the NTT Docomo Red Hurricanes of the Top League in 2020-2021. The AI development software uses NNC (Neural Network Console) to create a CNN model. And AI is evaluated by obtaining learning curves and confusion matrices. In a study conducted in 2020-2021, training was performed using the developed AI with 73 pieces of teacher data and 32 pieces of validation data as input, and the correct response rate was 6.25%. This could be attributed to the small amount of teacher data and the recognition rate of each tackle waveform. In this report, we summarize the series of steps from the creation of teacher data to the development, execution, and evaluation of the AI.

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  • Kazuharu SUGITA, Naoto MIYAMOTO, Masaki TAKEDA
    Session ID: B-4-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Running speed, stride length, and step frequency of a 400 m track and field run were measured using a high-precision kinematic global navigation satellite system (GNSS, 100 Hz). One subject (men, 22 years old, 400 m runner) was participated. GNSS antenna was attached to the top of the head using head gear and the subject was tried to run maximally for 400 m. The stride length and cycle time were determined from the change in the height of the head position. Lowest head position was seen at the timing of the foot landing during running. The distance and time were analyzed between every of foot landing during 400 m. Video was recorded from the back ward position of the runner Video recording and two-dimensional analysis were conducted in the last part of 10 m section to evaluate the validity of the time, stride length and step frequency measured by GNSS. The time, stride length, and step frequency between steps at last 10 m part measured by both GNSS and video were perfectly consistent (Speed: 2.54 vs 2.52 sec; Average per step: 0.32 vs 0.32 sec; step frequency: 3.15 vs 3.18 Hz). The analysis of running speed was measured with high accuracy. The stride length and step frequency were perfectly matched between the GNSS and video data based on the head change pattern.

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  • Yuta KAWASAKI, Ami OGAWA, Hidetoshi TAKAHASHI
    Session ID: B-5-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The ground reaction force (GRF) is one of the important factors in clarifying human movement, and a force plate is widely used for measuring GRF. This paper describes the force plate with seven springs and four non-contact displacement sensors. The proposed measurement principle allows for easy changes in shape and physical properties. When the GRF is applied to the force plate, the GRF is evaluated from the vertical and horizontal displacement of the top surface plate. The non-contact displacement sensors are composed of the magnet and planar coil. The force plate’s resonant frequency was 133 Hz. The calibration experiments show that vertical and horizontal forces and moments could be measured independently. The positional error of vertical force was 5% to −5%, and the resolutions were 1.95 N and 2.06 N in the anterior-posterior and vertical directions, respectively. Furthermore, the GRF waveform characteristics measured with a force plate were similar to the waveform of a normal gait.

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  • Kenichiro SHIMAZAKI, Akihito NAKAI, Hidetoshi TAKAHASHI
    Session ID: B-5-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    In this study, the forces applied to the sole during walking, jogging, and running were evaluated using Shokkaku-shoes that are equipped with MEMS 6-axis force sensors and acceleration/gyro sensors in their insoles. The MEMS 6-axis force sensors were placed at the thenar, the hypothenar, and the heel, and the acceleration/gyro sensor was placed at the center of the sole. Measurements were conducted on an athletics track over approximately 30 m for each movement. The data were analyzed for the three axial forces at the thenar, the hypothenar, and the heel. Then, it was found that the vertical forces in the forefoot increased as the motion became close to running, and the ground contact time gradually became shorter. Only braking forces were observed in walking, and propulsive force was detected only in the jogging and running motion unlike the typical GRF measurements using force plates.

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  • Yuya TAKAHASHI, Yoshihiro SASAKI, Takeshi YAMAGUCHI
    Session ID: B-5-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    There is a demand for the development of a ground reaction force measurement system that is not subject to location restrictions. In the current study, we developed a sole sensor system equipped with four high-capacity compact 3-axis force sensors using a Cr-N thin film. Using the sole sensor system, time-series data of the three-directional ground reaction forces during straight walking was estimated. Two models, a multiple regression analysis model and a Gaussian process regression model, were used for the estimation. The % root mean square error (%RMSE) and R2 values in the multiple regression analysis were 14.3 % and 0.419 in average in the left-and-right directions, respectively. The %RMSE and R2 values in the anteroposterior direction were 8.0 % and 0.869 in average, respectively, and those in the vertical direction were 8.2 % and 0.801 in average, respectively. The %RMSE and R2 values in the Gaussian process regression were 13.6 % and 0.458 in average in the left-and-right directions, respectively. The %RMSE and R2 values in the anteroposterior direction were 6.5 % and 0.891 in average, respectively, and those in the vertical direction were 4.8 % and 0.910 in average, respectively. In addition, in both models, the estimation accuracy in the 0-20% stance phase, which corresponds to the heel sensor contacting period, was lower than that in other stance phases.

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  • Akihito NAKAI, Akinori NAGANO, Hiroki KISHIKU, Isao SHIMOYAMA
    Session ID: B-5-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    We developed "Shokac-shoes" by placing three MEMS 6-axis force-torque sensors and a 6-axis inertial sensor on the insole of each shoe. Sensor data acquired by the “Shokac-shoes” were transferred to the smartphone via Bluetooth and then uploaded to the cloud server. Two AI analysis models were introduced to estimate the ground reaction force (GRF) and foot lift height from the limited data of 24 sensors. One was constructed using deep neural network for estimating GRF, and another was a combination of convolutional neural network and bidirectional LSTM (Long Short-Term Memory) for estimating foot lift height. It was confirmed that GRF and foot lift height could be estimated with validity by inputting time-series sensor data into the constructed AI models. The time required for AI models to present the estimated result to the user was about 5 seconds, which was confirmed to be short enough for practical use as the waiting time in the field of gait analysis. It is expected that the reduction of data costs by using “Shokac-shoes” will further promote research in various fields such as sports, healthcare and medicine.

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  • Rei IBATA, Kazuhiro FUJISAKI, Kazuhiko SASAGAWA
    Session ID: B-6-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Evaluations of muscle activities are important in the studies of motion analysis as human performance surveys. Force-myography (FMG), which has proposed as a similar objective to electromyography (EMG), has been applied in motion analysis focusing on the muscular activities. In this study, the usefulness of FMG for physical load measurements in repeated self-weight training was investigated in comparison with EMG. The muscle activities of the right rectus femoris were measured by each method when the subjects performed several patterns of squat motions. It was found that the intensity of muscle activity increased with increasing the load. In addition, when using the pressure sensing FMG devices, the effect of pumping up due to overuse of muscles was also found during the squat motion. By using FMG measurements, there is a possibility to evaluate conveniently the muscle activity during bodyweight training.

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  • Kaito MITANI, Makoto AYABE, Miyu YAMADA, Kazuhiro MORIMURA, Hideaki KU ...
    Session ID: B-6-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The present investigation aimed to develop a novel double product (DP) assessment using a pulse wave during the cycle-ergometer submaximal graded test (GXT). Young, healthy males were enrolled in the study. The exercise intensity was increased to 10 watts per minute after the 2-min warm-up period. The heart rate (HR), systolic blood pressure (SBP), and pulse wave were obtained continuously during the experimental period. A standardized device (TangoM2, SunTech Medical, North Carolina) was used for the HR and SBP measurements; the product of HR and SBP determined was used to evaluate the DP. The pulse wave was obtained at 1K Hz from the fingertip, and the pulse rate (PR) was analyzed. Thereafter, A-wave and the integration of pulse waveform were analyzed as a new index for the SBP (NSBPa and NSBPi, respectively). Furthermore, the products of PR and SBPa or SBPi were defined as the novel index of DP (NDPa and NDPi, respectively). There were significant correlation between PR and HR (p<0.05); furthermore, NSBPa and NSBPi correlated considerably with SBP (p<0.05), and NDPa and NDPi were significantly associated with DP (p<0.05). The present investigation revealed that the pulse wave could estimate the HR, SBP, and DP during the GXT in young male adults.

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  • Miyu YAMADA, Makoto AYABE, Kaito MITANI
    Session ID: B-6-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The present investigation aimed to develop a novel method of spontaneous laughter (SL) assessment based on heart rate variability (HRV) and lumbar accelerometry under free-living conditions. The subjects of the present investigation were ten healthy young men. The investigation consisted of three 15-min experimental periods after the resting period and 5 h of free-living conditions. The three experimental periods included light-intensity aerobic exercise (LAE), moderate-intensity aerobic exercise (MAE), or watching comedy movie inducing SL (SLA), and were randomly ordered across three separate days. During SLA, the subjects watched comedy movies. The autonomic nervous system (ANS) activity was measured using continuous heart rate (HR) responses over the investigation period; the total power, low frequency (LF: 0.035 to 0.15 Hz), and high frequency (HF: 0.15 to 0.4) components were obtained using frequency analysis. The LF and HF were normalized by total power (nHF, nLF), and the LF was divided by HF to obtain a sympathetic activity index (LF/HF). SLA increased sympathetic nerve activity without an increase in heart rate compared to the resting state. The results of the preset investigation suggested that the combination of acceleration with heart rate and the autonomic nerve activity can improve the accuracy for estimating the SLA under the free-living condition.

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  • Kosuke OKAZAKI, Nobutaka TSUJIUCHI, Akihito ITO, Kosuke ITO, Masahiko ...
    Session ID: B-7-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Golf is a sport that can be enjoyed by people of all ages. The appeal of golf is not only the competition of scores, but also the feeling of satisfaction that comes from hitting an accurate shot. For accurate shots, it is necessary to use a club that is suitable for each individual swing. Just as the swing is different for each golfer, the deformation behavior of the shaft during the swinging motion is also considered to be different for each golfer. Therefore, several researches has been conducted on swing motion and shaft deformation behavior to select the appropriate club for swinging, but the swing motion that makes a difference in deformation behavior has not been clarified. Therefore, the objective of this study is to extract the golfer's swing motion that gives characteristic differences in the deformation behavior of the shaft. First, a simulation model that reproduced the deformation behavior of the shaft was constructed using FEM. The deformation behavior of the shaft was calculated using the simulation model, and differences in deformation behavior among each golfer. Next, wavelet analysis was applied to the golfer's swing motion to confirm the temporal variation of the frequency band during the swing motion. Finally, the results of the wavelet analysis were used to extract differences in the swinging motion that cause differences in the deformation behavior.

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  • Kosuke OKAZAKI, Nobutaka TSUJIUCHI, Akihito ITO, Kosuke ITO, Hiroshi K ...
    Session ID: B-7-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Golf is a sport that can be enjoyed by people of all ages. The appeal of golf is not only the competition of scores, but also the feeling of satisfaction that comes from hitting an accurate shot. For accurate shots, it is necessary not only to use clubs suitable for the golfer’s swings, but also to improve swinging motion. Many golfers wish to improve their swing, but it is difficult to do so easily because the swinging motion is complex and because each golfer swing is unique. Therefore, the purpose of this study is to propose a golf swing improvement method for beginners and intermediate golfers based on the hypothesis that beginners and intermediate golfers do not understand the coordinated movements of the body during the golf swing. First, we measured the basic movements related to the golf swing, called "exercise movements," of beginners and intermediate players. After the exercise movements were measured, the instructor provided instruction to improve the exercise movements. After the improvement of the exercise movements was confirmed, singular value decomposition was performed on the exercise movements before and after the improvement, the exercise movements were decomposed into multiple cooperative movements, and the original and improved cooperative movements were compared. Finally, we compared the swing movements before and after the exercise movements and investigated the effect of the improvement of the exercise movements on the swing movements.

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  • Tomohiro HASHIGUCHI
    Session ID: B-7-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The purpose of this study is to quantify the effects of various factors on player performance and to obtain useful suggestions for racket designing by constructing a three-dimensional simulation model of badminton swing motion. The racket model consists of a shaft section divided into four rigid segments, with virtual joints with rotational springs between adjacent segments, and elastic torques acting in response to angular displacement and angular velocity to represent shaft bending. For the upper limb, the hand, forearm, and upper arm were modeled as a three-segment rigid body model. The torque acting on the virtual joints of each joint and grip section is controlled by PD control, which sets the control gain according to the joint angle and angular velocity calculated based on the observed values for the input joint torque, to obtain a joint torque reduces the error between the motion generated by the simulation and the actual motion. The results obtained from the simulations, effects of shaft design factors on various evaluation quantities were calculated. Regarding the validity of the model, although the obtained model represented the racket head speed during the swing well, it was observed that the error near impact was larger than that of the actual measurement.

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  • Kenta MATSUMOTO, Nobutaka TSUJIUCHI, Akihito ITO, Hiroshi KOBAYASHI, M ...
    Session ID: B-7-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    In this study, we tried to analyze the feature of golf swings using by singular value decomposition (SVD). For extracting cooperative action from different swings, we conducted experiment of acquiring swing data. Subjects were 2 beginners and 5 intermediates, 4 expert golfers for analyzing the swing features. We measured each golfer’s swings by motion capture system (VICON). We built observance matrix from acquired positional data and we conducted SVD on this observance matrix. By conducting SVD, we extracted cooperative action as some independent modes. Then, as for showing the swing features of each golfer, we computed correlation coefficient by space basis which is one of the independent modes of SVD. As a result, we reached the following conclusion that we could show swing features of individual expert golfers from 3rd to 5th mode and the difference experts and intermediates, beginners using by the correlation coefficient computed from 3rd to 5th mode.

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  • Tomohito NAKATSUGAWA, Yuya EZAWA, Takeo MARUYAMA
    Session ID: B-9-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Forefoot torsional stiffness relative to rearfoot has been suggested the effects on foot dynamics during walking. However, there is no study that examined the effects on foot dynamics during running. The purpose of this study was to clarify the relationship between foot torsional stiffness and foot dynamics during running. 8 healthy rearfoot striker students (5 males and 3 females) were measured foot torsional stiffness. In addition, the participants’ rearfoot and forefoot kinematics during stance phase of running were collected using a three-dimensional motion analysis system. Pearson product-moment correlation coefficients revealed that foot torsional stiffness was significantly positively correlated with rearfoot excursion in sagittal plane (r = 0.760; p = 0.029) and forefoot excursion in transverse plane (r = 0.709; p = 0.049) during the propulsive phase. However, foot torsional stiffness was not associated with rearfoot kinematics or loading rate during the absorption phase. These results suggest that foot torsional stiffness is not associated with absorption phase during running with rearfoot strike.

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  • Ryoko HIDAKA, Sekiya KOIKE
    Session ID: B-9-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    In order to improve performance and prevent foot disorders, it is necessary to understand the characteristics of the foot deformation and to study the relationship between mechanical properties. However, most studies regarding the foot deformation and mechanical properties during movement have focused on walking and running along a straight line, and there are no studies on lateral movements such as cutting maneuver, which are usually seen in ball games. The aim of this study was to investigate the effect of changes of direction angle on foot arch deformation by quantifying foot arch deformation during cutting maneuver, which are expected to have different deformation characteristics compared to walking and straight running. The results of this study suggest that: 1. they have different deformation patterns during ground contact between the medial longitudinal arch, and midfoot and forefoot transverse arch; 2. compared with straight running, the deformation of the medial longitudinal arch increased, and the deformation of the midfoot and forefoot transverse arch decreased during cutting maneuver.

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  • Naoto MORITA, Nobuhito UCHIDA, Shigeru WESUGI
    Session ID: B-9-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Recently, there are a lot of researches to analyze motion in sports to improve motor skills. It is hard to learn ideal movement by simply analyzing data especially in sprint running, which requires complex movements in a short period of time. In this research, the authors have worked on the method to acquire the aimed movement through physical experience. In sprint running, it is said that the coordination between trunk and pelvic rotation generates more efficient horizontal floor reaction force for increasing speed. Therefore, we devised two experimental devices to reduce the phase difference between trunk and pelvic rotation. The first one is tension applying device to increase muscular activity for pelvic rotation with force by pulling a wire attached to both sides of the waist. Second one is skin shear deformation device to support fine adjustment of pelvic rotation by applying shear force to skin around pelvis. We confirmed that these devices satisfied experimental requirements, and it was suggested that the devices could have an effect on the waist rotation for sprint running.

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  • Harutoshi YUKAWA, Minato ABE, Shozo KAWAMURA
    Session ID: B-9-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Shock attenuation property of sports surfaces is especially important not only for the athlete’s performance but also for injury prevention. To evaluate the properties of the sports surfaces, some sport governing bodies often adopt friction tests and shock attenuation tests to determine the horizontal and vertical characteristics, respectively. Although the diagonal impacts are often observed in athletic sports, shock attenuation test treats only the vertical impact test. Therefore, we developed a two-dimensional impact test device for examining the two-dimensional cushioning characteristics of sports surfaces in previous studies. To produce a simultaneous two-dimensional force against a test specimen, we incorporated a parallelogram linkage in the measuring system. In this study, we conducted impact tests using spike pins for long-distance running competitions, assuming the use of actual sports surfaces, and verified their validity in surface deformations by using a high-speed camera.

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  • Taiga YAMASAKI, Xin XIN, Shinsaku IZUMI, Motoyuki NAWA, Kazuie NISHIWA ...
    Session ID: C-1-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    A motor control model is developed for a double-leg circle on a pommel horse, which takes into account the switching of support between two pommels and three-dimensional rotation of the whole body of a gymnast. The whole body is modeled as a single rigid segment, and a mechanism for changing the position of the shoulder joint relative to the body segment is incorporated. The control objective is represented by a combination of physically interpretable conditions, and a control model is proposed to achieve this objective. Simulation results are presented to show that the model can reproduce motion qualitatively similar to actual circles.

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  • Tadashi SHIOYA
    Session ID: C-1-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Samba Bounce is analysed in the mechanical point of view. There have been confusion and misunderstanding among the dance teachers as they explain the bounce action designating the height of the body and the force in relation to the music timing. Bounce action has been explained in the syllabus using special terms such as “minimal weight”, “part weight”, “without weight but with pressure” and other terms. These confusions and somewhat ambiguous terms in the scientific sense are clearly resolved by the present mechanical analysis and interpreted with newly introduced concept of “static weight” and “dynamic weight”. In the presentation, the bounce movement is expressed as a simple harmonic vertical motion. The height position, vertical velocity and acceleration of dancer’s body are shown with the forces between the floor and each foot. The difference between dancer’s feeling and observer’s feeling is also explained. figures.

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  • Yaeko NOBE, Hisashi UCHIYAMA, Satoshi OHASHI, Masahito NAGAMORI, Taken ...
    Session ID: C-2-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    In order to realize a healthy and long-lived society, it is recommended to exercise for the purpose of health promotion and exercise therapy. Exercise rehabilitation, especially for patients with heart disease and respiratory disease, helps them avoid being bedridden and plays a major role in maintaining their QOL in daily life. On the other hand, excessive exercise load is contraindicated because it may exacerbate symptoms. Therefore, cardiopulmonary exercise training (CPX) is necessary to understand changes in gas exchange associated with breathing and circulation, and to determine the Anaerobic Threshold (AT), which is an indicator of optimal exercise load intensity. AT is the addition of an anaerobic energy production mechanism to an aerobic energy production mechanism. CPX is performed at the time of initial determination of AT and after implementation of rehabilitation to verify its effect and review AT. AT determination generally requires 10-15 minutes of gradual incremental workload. In this study, based on the AT intensity determined by gradual incremental workload, the subject performed his 3-5 min quantitative resistance exercise on a bicycle ergometer. During that time, the collected expired air was measured with a breath-by-breath type expired gas analyzer. Then, using physical work, we verified the change of V-slope due to the difference in load intensity. As a result, AT could be estimated from the slope from the inflection point of the V-slope of the constant load. This method makes it possible to shorten the CPX time when revising AT, leading to a reduction in the burden on the subject.

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  • Kazuo UCHIDA, Tsuguya SAITO, Daisuke KONDO
    Session ID: C-4-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    This paper proposes a method for estimating the movement of a wheelchair using inertial sensors, even in the absence of GPS. A plant model was constructed by a kinematics model which includes wheelchair’s body section and two wheels, and constraint equations of differential type two-wheeled vehicle model. Simulating wheelchair tennis motion was performed and measured with an inertial sensor and optical motion capture. By applying the extended Kalman filter to the model described above, the wheelchair motion was accurately estimated for 20 seconds in duration.

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  • Hajime TAKANO, Satoshi OHASHI, Akira SHIONOYA, Masahito NAGAMORI
    Session ID: C-4-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The sidewalks we use in our daily lives are made of various surface materials, such as asphalt pavement and concrete pavement. In terms of barrier-free access, Braille blocks are provided on the sidewalks. Barrier-free maps are also available to assist wheelchair users in their daily lives. The Barrier-Free Map shows the location of wheelchair-accessible restrooms and the status of barrier-free facilities at stations and stores. However, it does not indicate the type of road surface, deterioration conditions and other information necessary for wheelchair users to travel. Wheelchair users may experience problems in riding and driving due to uneven road surfaces, bumps, and joints between blocks. However, it is difficult to select a comfortable travel route in advance because the road surface condition cannot be determined without visiting the road. In addition, wheelchair users have the problem of not knowing whether they can drive on their own or need assistance without directly checking the road surface conditions. If the road conditions can be provided to wheelchair users in advance, they can take the most appropriate route. In this study, we report on a road surface estimation method that uses the vibrations generated during wheelchair driving. The following six types of road surfaces were used in the experiment. These road surfaces were wood flooring, two types of asphalt pavement, two types of interlocking block pavement, and a wood deck floor. The wheelchair used was equipped with four vibration sensors for data collection. The vibration sensors were mounted on a frame with casters and tires on its axis. The vibration data collected in the experiment was the result of a 20 [m] straight run on each of the road surfaces. For road surface estimation, a learning model was built for deep learning using spectrum images for the vibration data. As a result, five types of road surfaces could be discriminated with an accuracy of more than 80%.

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  • Izuru OKAJIMA, Akira SHIONOYA, Satoshi OHASHI, Hisashi UCHIYAMA, Masah ...
    Session ID: C-5-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    While Para-badminton has become a new sport for the Tokyo 2020 Paralympic Games and attention to Para-badminton is increasing, there is still little research on the performance and materials of badminton wheelchairs. The purpose of this study was to evaluate the driving performance of a conventional badminton wheelchair made of Mg alloy and a lighter weight badminton wheelchair made of Al alloy, and measurements were made using an inertial sensor for comparison. The inertial sensors can record data at 1 kHz. Inertial sensors were attached to the drive wheels of the two types of badminton wheelchairs to measure the forward and backward rowing motions, and the time and speed required for these motions were compared. The measurement site was a gymnasium, and the subjects were three able-bodied students. As a result, there was almost no difference in the maximum speed, and the time required for the forward rowing motion tended to be smaller on the Al wheel than on the Mg wheel.

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  • Ryoga NAKANISHI, Motomichi SONOBE, Kiyoshi HIROSE
    Session ID: C-6-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Human gait analysis generally needs acceleration at the center of joints where inertial measurement units (IMU) cannot be attached. The joint acceleration estimation requires the position vectors from the IMU to the center of the joint in the sensor coordinate system. Past studies have proposed a method to estimate the position vector of the joint center from two IMUs attached to two rigid bodies, respectively. The idea is based on the equality of a joint center acceleration estimated from two IMUs. However, the estimation accuracy of the position vector depends on the calibration movement. The purpose of this study is to verify the accuracy of the position vector from a lower leg IMU to the ankle joint with calibration movements. We determined the movements as a squat movement and a unidirectional knee rotating movement and compared their accuracy. We assumed that the ankle joint keeps resting throughout the calibration movements. The result demonstrated that the accuracy was better for the unidirectional knee rotation movement and dependent on the quality of the calibration movement.

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  • Akihiro SUZUKI, Sena ISHII, Masao MORI
    Session ID: C-6-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The number of elderly people with dementia is increasing every year and becoming a social problem. As symptoms of dementia progress, physical function declines and physical activity decreases, creating a vicious cycle. However, in the case of mild cognitive impairment (MCI), half of all dementia patients can recover to a normal state through treatment. Early detection of dementia is therefore essential. Therefore, we focused on gait disturbance, one of the symptoms of dementia. As an experimental method, we conducted an outdoor walking experiment using an insole with a pressure sensor placed and a lumbar acceleration/angular velocity sensor. Ten cognitive function estimation parameters were extracted from the obtained foot pressure data and lumbar acceleration/angular velocity data. The Mini-Mental State Examination(MMSE) was also used to measure the subjects' cognitive function. Multiple regression analysis and binomial logistic regression analysis were performed to examine the relationship between cognitive function and the estimated parameters of cognitive function. As a result, highly accurate cognitive function estimation equations were obtained for the MCI group. In addition, discriminant equations were obtained with high accuracy for healthy subjects and MCI, and for dementia and healthy subjects with MCI. This study is expected to confirm the decline of cognitive function from walking behavior in daily activities and to be useful for early detection and treatment of dementia.

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  • Yuga TAKAHASHI, Iwori TAKEDA, Hiroshi ONODERA, Takeshi YAMAGUCHI
    Session ID: C-6-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    To prevent back pain during load lifting, assist suits have been developed to reduce physical load by assisting human motion. There are two methods of lifting heavy objects: the stoop method and the squat method. Assistive suits to facilitate the squat method, which reduces the burden on the lower back, have not yet been put to practical use. Therefore, there is a need to develop assistive suits that are lightweight and do not require power. In this study, we developed a short leg orthosis using a leaf spring made of carbon fiber reinforced plastic (CFRP), and conducted lifting and unloading experiments of heavy objects while wearing the orthosis. We then investigated the work support effects of wearing the orthosis based on measurements of lower limb joint power using a three-dimensional motion analysis system and surface electromyography measurements. The results showed that joint angles and power at the ankle and knee joints during lifting was reduced, and joint angles at the ankle and knee joints and power at the knee joint during unloading was reduced by using the orthosis. In both lifting up and unloading, muscle use of the rectus femoris and gastrocnemius muscles decreased, while spinal muscles showed an increasing trend. In addition, muscle synergy analysis revealed two muscle synergies in both lifting up and unloading, indicating that wearing the orthosis reduced lower limb strain during lifting up, and reduced lower back and lower limb strain during unloading and standing up.

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  • Norikazu SHODO, Reima IWATSU, Naoya TAKAHASHI, Takeshi MIYAZAKI
    Session ID: C-8-1
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The flow past an archery bare-shaft arrow is computed by using a CFD code. Two types of arrow point, i.e., bullet point and streamlined point, are simulated for the Reynolds number, based on the shaft diameter, in a range 1.0 × 104Re ≤ 2.0 × 104, and the attack angle, α, varied between 0.0° and 1.0°. The flow field around the arrow point and the surface of shaft is visualized mainly for the quasi-steady state flows. The drag coefficient CD is computed for the ranges of Re and α, and compared with the previous analytical, as well as experimental values.The results of the present study appears to suggest that for the arrow with bullet point and non-zero attack angle, the onset of unsteadiness is triggered by the separation at the joint portion between point and shaft, while for the arrow with streamlined point, unsteadiness manifests at the arrow tail and gradually spread upstream on the surface of the shaft.

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  • Kohei MORIYAMA, Hiroo OKANAGA
    Session ID: C-8-4
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    The surface of a golf ball is covered with numerous dimples to increase the flying distance. It is known that it is important to indicate the state of these dimples in terms of occupancy and volume ratio. Past studies have also shown that the conical shape has the lowest drag coefficient when the base shape of the dimple is changed to a cone or a conical base and the drag force is measured at no-rotation. Therefore, in this study, lift and drag force measurement experiments during rotation are conducted in a wind tunnel using model balls with dimple base shapes that are not only spherical, but also conical or conical in shape. Then, flight trajectory simulations will be performed with the obtained results to clarify the effects of dimple occupancy, volume ratio, and base shape. Then, we will discover the items that are particularly important for designing the most flying balls.

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  • Masashi NOTOYA, Michihiro SATO, Tomo CHIDA, Arisa OZAKI
    Session ID: C-9-2
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Research Center for Winter Sports Science of Kitami Institute of Technology was established in 2016. Curling and alpine skiing are researched at this center located in a snowy and heavy cold area. In research on alpine skiing, we are conducting experiments to adjust the ski boots and improve their skills of Japanese skiers. Previous experimental studies have shown that the large inclination angle and a fast inclination angular velocity during turns have a great influence on the improvement of downhill speed in alpine skiing (2) ~ (5). Furthermore, it has been found that attaching parts to the underside of the footbed inside the ski boot changes the inclination angle and inclination angular velocity. In this study, we used the ski simulator "SkyTech" at this center and "the real-time experimental data collection system" with a pressure sensor and the inclination angle measuring devices, and performed an experiment to adjustment of depression angle. And we calculated the parameters for evaluating the athletes’ turn movements from the obtained experimental data, and investigated the quantitative evaluation of alpine skiers’ skill of turning motion.

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  • Shunsuke YOKOI, Shotaro ASAKURA, Hiroaki HASEGAWA, Masahide MURAKAMI
    Session ID: C-9-3
    Published: 2022
    Released on J-STAGE: May 25, 2023
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    Ski jumping is a sport in which the competitor is judged based on the flight form and flight distance; therefore, ski jumpers attempt to fly as far as possible upon take-off. The fabric used for ski jumping suits plays a crucial role in achieving favorable aerodynamic characteristics. It is generally assumed that ski jumping suits made from fabrics with low air permeability will have favorable aerodynamic characteristics. However, the effect of the air permeability of ski jumping suits on aerodynamic characteristics has not been completely clarified yet. The purpose of this study is to investigate the effect of air permeability on the aerodynamic characteristics of ski jumping suits. Wind tunnel experiments were carried out on the NACA airfoil clothed with ski jumping suit fabrics of different air permeability. The stall delay occurs and drag force decreases with an increase in air permeability. It was confirmed that the stall characteristics are greatly affected by the air permeability.

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